1. Field of the Invention
Embodiments of the invention relate to the field of optical communication devices. More particularly, the present invention relates to an optical circuit providing a dual output laser source used for an optical communication system.
2. Discussion of Related Art
Wavelength division multiplexed (WDM) optical communication systems are known in which multiple optical signals, each having a different wavelength, are combined onto a single optical fiber. Such systems typically include a laser light source associated with each wavelength, a modulator configured to modulate the output of the laser, and an optical combiner to combine each of the modulated outputs. Conventionally, WDM systems have been constructed from discrete components. For example, the lasers, modulators and combiners have been packaged separately and mounted on a printed circuit board. More recently, however, many WDM components including transmitters, receivers and passive devices have been integrated onto a single chip also referred to as a photonic integrated circuit (PIC) chip.
Typically, these transmitters include a plurality of semiconductor lasers which provide continuous wave (CW) light signals to an optical circuit. Each of these lasers supply light at a particular wavelength where each wavelength is associated with a respective optical channel within a known WDM communications channel grid (e.g. ITU). Each of a plurality of modulators receive the CW light signals as well as respective data streams and output modulated optical signals at each particular wavelength. One type of semiconductor laser is a distributed feedback (DFB) laser which employs a diffraction grating structure that couples both forward and backward propagating coherent light produced in an active region of a semiconductor substrate. Lasers are considered active components because they require electrical power to function. Additionally, passive components including splitters, combiners, waveguides, etc., do not require power to operate, but do occupy valuable space on a PIC chip. Thus, as the requirement to transmit more data using smaller device sizes becomes increasingly important, there is a need to produce transmitters, receivers and the like using fewer discrete components while minimizing power requirements all at reduced costs.